Method for the synthesis of diacids or diesters from natural fatty acids and/or esters

ABSTRACT

The invention relates to a process for the synthesis of diacids or diesters of general formula ROOC—(CH 2 ) x —COOR, in which n is an integer between 5 and 14, R is either H or an alkyl radical of 1 to 4 carbon atoms, from natural long-chain monounsaturated fatty acids or esters including at least 10 adjacent carbon atoms per molecule of the general formula CH 3 —(CH 2 ) n —CHR 1 —CH 2 —CH═CH—(CH 2 ) p —COOR, in which R is H or an alkyl radical with 1 to 4 carbon atoms, R 1  is either H or OH, and n and p, which are equal or different and are indices between 2 and 11. The method comprises: during a first step, converting the natural fatty acid or ester by pyrolysis or by ethenolysis, into a ω-monounsaturated fatty acid or ester of the general formula CH 2 ═CH—(CH 2 ) m —COOR, in which m is equal to p or p+1, depending on the nature of the processed fatty acid/ester and the conversion used; during a second step, submitting the product thus obtained to a metathesis or homometathesis reaction for obtaining a compound of the general formula ROOC—(CH 2 ) m —CH═CH—(CH 2 ) m —COOR, or cross-metathesis with a compound of formula R 2 OOC—(CH 2 ) r —CH═CH—R 3 , in which R 2  is either H or an alkyl radical front with 1 to 4 carbon atoms, r is either 0 or 1 or 2 and R 3  is H, CH 3  or COOR 2 , thus defining a cyclic or molecule or not, in order to obtain an unsaturated compound of the general formula ROOC—(CH 2 ) m —CH═CH—(CH 2 ) r —COOR 2 , and during a third step, converting the unsaturated compound into a saturated compound by hydrogenation of the double bond.

The invention is targeted at a process for the synthesis by metathesisof saturated long-chain diacids or diesters starting from amonounsaturated fatty acid or fatty ester which is either natural ororiginates from the direct conversion of a natural oil.

Diacids are obtained industrially by various methods, all of which,however, exhibit some disadvantages. A great variety of these methods isenlarged upon in the Kirk-Othmer Encyclopedia, Vol. A8, pages 523-539.

It is possible to distinguish therein methods by degradation, such asozonolysis or oxidation, of vegetable fatty acids.

The ozonolysis of oleic acid, of petroselinic acid and of erucic acidmakes it possible to respectively produce the diacids comprising 9, 6and 13 carbon atoms according to the above reaction process forpetroselinic acid.

Another example is the cleavage of ricinoleic acid by the action ofsodium hydroxide at a temperature of greater than 180° C. This method,used industrially, makes it possible to obtain the diacid comprising 10carbon atoms.

The same method, as illustrated in the scheme below, can be applied tolesquerolic acid and results in the formation of a diacid comprising 12carbon atoms.This method exhibits the advantage of using renewable starting materialsbut is restricted essentially to the C₁₀ diacid, lesquerolic acid beingstill not very widespread, and thus this method is relatively littleused.

Mention may also be made of the oxidative degradation of monocarboxylicacids by the action of N₂O₄. The oxidation of stearic acid makes itpossible to obtain a mixture of sebacic acid and of caprylic acid;suberic acid can be obtained from palmitic acid.

It is also possible to obtain diacids from smaller molecules by usingvariant techniques of carbonylation.

Finally, mention may be made of the bacterial fermentation of paraffins,a well known method which makes it possible to obtain numerous diacidsof variable chain length. However, this method does not make it possibleto obtain diacids with a length of greater than 16 carbon atoms as theparaffins then have a melting point which is far too high for conversionto be possible. Another major disadvantage is that the bacteria consumea portion of the paraffins in order to provide for their growth,resulting in low yields and in the need to purify the products.

In the polymer industry, in particular for the production of polyamidesof diacids/diamines type or of industrial polymers, it is necessary tohave available a whole range of diacids as starting materials, whichdiacids can in addition be converted to diamines of the same chainlength by a simple chemical reaction.

It is therefore necessary to find a type of process which makes itpossible to obtain a virtually complete range of diacids and which, inaddition, uses renewable materials of natural origin.

The object of the invention is a process for the production of a wholerange of saturated diacids or diesters of general formulaROOC—(CH₂)_(x)—COOR starting from fatty acids of natural origin.

The solution provided consists in carrying out the operation startingfrom long-chain natural monounsaturated fatty acids. Long-chain naturalfatty acid is understood to mean an acid resulting from plant or animalsources, including algae, more generally from the plant kingdom, whichare thus renewable, comprising at least 10 and preferably at least 14carbon atoms per molecule.

Mention may be made, as examples of such acids, of the C₁₀ acidsobtusilic (cis-4-decenoic) acid and caproleic (cis-9-decenoic) acid, theC₁₂ acids lauroleic (cis-5-dodecenoic) acid and linderic(cis-4-dodecenoic) acid, the C₁₄ acids myristoleic (cis-9-tetradecenoic)acid, physeteric (cis-5-tetradecenoic) acid and tsuzuic(cis-4-tetradecenoic) acid, the C₁₆ acid palmitoleic(cis-9-hexadecenoic) acid, the C₁₈ acids oleic (cis-9-octadecenoic)acid, elaidic (trans-9-octadecenoic) acid, petroselinic(cis-6-octadecenoic) acid, vaccenic (cis-11-octadecenoic) acid andricinoleic (12-hydroxy-cis-9-octadecenoic) acid, the C₂₀ acids gadoleic(cis-9-eicosenoic) acid, gondoic (cis-11-eicosenoic) acid,cis-5-eicosenoic acid and lesquerolic (14-hydroxy-cis-11-eicosenoic)acid, and the C₂₂ acids cetoleic (cis-11-docosenoic) acid and erucic(cis-13-docosenoic) acid.

These various acids result from the vegetable oils extracted fromvarious plants, such as sunflower, rape, castor oil plant, bladderpod,olive, soya, palm tree, coriander, celery, dill, carrot, fennel orLimnanthes alba (meadowfoam).

They also result from the terrestrial or marine animal world and, in thelatter case, both in the form of fish or mammals, on the one hand, andof algae, on the other hand. They are in general fats originating fromruminants, from fish, such as the cod, or from marine mammals, such aswhales or dolphins.

The invention is targeted at a process for the synthesis of diacids ordiesters of general formula ROOC—(CH₂)_(x)—COOR, in which x representsan integer between 5 and 24 and R is either H or an alkyl radical of 1to 4 carbon atoms, starting from long-chain natural monounsaturatedfatty acids or esters comprising at least 10 adjacent carbon atoms permolecule, of formula CH₃—(CH₂)_(n)—CHR₁—CH₂—CH═CH—(CH₂)_(p)—COOR, inwhich R represents H or an alkyl radical comprising from 1 to 4 carbonatoms, R₁ is either H or OH, and n and p, which are identical ordifferent, are indices between 2 and 11, preferably between 3 and 11,which consists, in a first stage, in converting said natural fatty acidor ester, either by pyrolysis or by ethenolysis (ethylenecross-metathesis), into an ω-monounsaturated fatty acid or ester ofgeneral formula CH₂═CH—(CH₂)_(m)—COOR, in which m is equal to p or p+1,depending on the nature of the fatty acid/ester treated and theconversion used, ethenolysis or pyrolysis, then, in a second stage, insubjecting the product thus obtained to a metathesis reaction, eitherhomometathesis, in order to obtain a compound of formulaROOC—(CH₂)_(m)—CH═CH—(CH₂), —COOR, or cross-metathesis with a compoundof formula R₂OOC—(CH₂)_(r)—CH═CH—R₃, in which R₂ is either H or an alkylradical comprising from 1 to 4 carbon atoms, r is either 0 or 1 or 2 andR₃ is H, CH₃ or COOR₂, in the last case forming a cyclic or noncyclicmolecule, in order to obtain an unsaturated compound of formulaROOC—(CH₂)_(m)—CH═CH—(CH₂)_(r)—COOR₂, and then, in a third stage, infinally converting, by hydrogenation of the double bond, the unsaturatedcompound to give a saturated compound.

The natural monounsaturated fatty acid or ester of general formulaCH₃—(CH₂)_(n)—CHOH—CH₂—CH═CH—(CH₂)_(p)—COOR can be subjected to apyrolysis reaction.

The acid or the ester of formula CH₂═CH—(CH₂)_(p+1)—COOR resulting fromthe first stage can be subjected to a homometathesis, the product ofwhich, ROOC—(CH₂)_(p+1)—CH═CH—(CH₂)_(p+1)—COOR is hydrogenated.

The acid or the ester of formula CH₂═CH—(CH₂)_(p+1)—COOR resulting fromthe first stage can be subjected to a cross-metathesis, the product ofwhich obtained is hydrogenated.

The natural monounsaturated fatty acid or ester of general formulaCH₃—(CH₂)_(n)—CHOH—CH₂—CH═CH—(CH₂)_(p)—COOR can be subjected to anethenolysis reaction.

The acid or the ester of formula CH₂═CH—(CH₂)_(p)—COOR resulting fromthe first stage can be subjected to a homometathesis, the product ofwhich, ROOC—(CH₂)_(p)—CH═CH—(CH₂)_(p)—COOR is hydrogenated.

The acid or the ester of formula CH₂═CH—(CH₂)_(p)—COOR resulting fromthe first stage can be subjected to a cross-metathesis, the product ofwhich obtained is hydrogenated.

The cross-metathesis is carried out with acrylic acid when R₂=H, x=0 andR₃=H.

In the case where x=1, R₂=H and R₃=CH₃, the compound isHOOC—CH₂—CH═CH—CH₃ and is obtained, for example, by hydroxycarbonylationof butadiene. In this case, during the cross-metathesis, propylene isproduced and is removed from the reaction medium.

Preferably, when R₃ is COOR₂, R₂OOC—(CH₂)_(r)—CH═CH—R₃ is a symmetricalmolecule with r=0. When R₃ is CH₃, R₂OOC—(CH₂)_(r)—CH═CH—R₃ reacts witha fatty acid by cross-metathesis and the reaction results in a diacidand a shorter fatty acid but also in propylene. The propylene is removedas it is formed from the reaction medium, which displaces the reactiontowards the desired products.

When R₂OOC—(CH₂)_(r)—CH═CH—COOR₂ forms a cyclic molecule, such as maleicanhydride, then the cross-metathesis results in an unsaturated fattyacid also comprising an anhydride functional group. The diacid and thefatty acid can be released by hydrolysis.

In the process of the invention, the fatty acid can be treated either inits acid form or in its ester form. The change from one form to theother is carried out by methenolysis, esterification or hydrolysis.

In the process of the invention, use is made of fatty acids or esters ofnatural origin, that is to say present in extracted oils or fats. Thelatter are in fact composed, in addition to the ester or acidparticipating in the reaction, of a mixture of esters or acids withsimilar formulae. By way of examples, palm oil comprises, in addition tooleic acid, linoleic acid; castor oil comprises, in addition toricinoleic acid, both oleic acid and linoleic acid; and rapeseed oilcomprises, in addition to oleic acid, simultaneously linoleic acid,linolenic acid and gadoleic acid. The presence of these diunsaturated orpolyunsaturated acids is not of major consequence with regard to theprogression of the process insofar as, during the first stage, in thecase of ethenolysis, linoleic acid will also form the ω-monounsaturatedfatty acid of general formula CH₂═CH—(CH₂)_(m)—COOR, with minor amountsof short dienes and of α-olefins. In the case of ricinoleic acid, thepyrolysis reaction will not convert these similar acids.

Examples of the synthesis of diacids are given below. All the mechanismsdetailed below illustrate, in order to facilitate the account, the acidformed. However, the metathesis is also effective with an ester and evenoften more effective, the medium generally being more anhydrous. In thesame way, the schemes illustrate reactions with the cis isomer of theacids (or esters); the mechanisms are also clearly applicable to thetrans isomers.

The C₆ diacid can be obtained from obtusilic (cis-4-decenoic) acid,linderic (cis-4-dodecenoic) acid and tsuzuic (cis-4-tetradecenoic) acidby carrying out an ethenolysis in the first stage, followed by across-metathesis with acrylic acid and then hydrogenation.

The C₇ diacid can be obtained from lauroleic (cis-5-dodecenoic) acid andphyseteric (cis-5-tetradecenoic) acid by an ethenolysis in the firststage, followed by a cross-metathesis with acrylic acid and thenhydrogenation.

The C₈ diacid can be obtained from obtusilic (cis-4-decenoic) acid,linderic (cis-4-dodecenoic) acid and tsuzuic (cis-4-tetradecenoic) acidby carrying out an ethenolysis in the first stage, followed by ahomometathesis, or from petroselinic acid by ethenolysis in the firststage, followed by a cross-metathesis with acrylic acid, in both casesbrought to completion by a hydrogenation.

The C₁₀ diacid can be obtained from lauroleic (cis-5-dodecenoic) acidand physeteric (cis-5-tetradecenoic) acid by an ethenolysis in the firststage, followed by homometathesis finished off by the hydrogenation.

The C₁₁ diacid can be obtained from oleic (cis-9-octadecenoic) acid,elaidic (trans-9-octadecenoic) acid, gadoleic (cis-9-eicosenoic) acidand myristoleic (cis-9-tetradecenoic) acid with an ethenolysis in thefirst stage, followed by a cross-metathesis with acrylic acid, in eachcase brought to completion by a hydrogenation. In the case of oleicacid, the following reaction process will be employed:

CH₃—(CH₂)₇—CH═CH—(CH₂)₇—COOH+CH₂═CH₂

CH₂═CH—(CH₂)₇—COOH+CH₂═CH—(CH₂)₇—C₃  1)

CH₂═CH—(CH₂)₇—COOH+HOOC—CH═CH₂

HOOC—CH═CH—(CH₂)₇—COOH+CH₂═CH₂  2)

HOOC—CH═CH—(CH₂)₇—COOH+H₂→HOOC—(CH₂)₉—COOH  3)

The reaction mechanism for this reaction is, in its various alternativeforms, illustrated by scheme 1 below

The C₁₂ diacid can be obtained from petroselinic acid and ricinoleicacid according to two different reaction mechanisms. Petroselinic(cis-6-octadecenoic) acid is converted by an ethenolysis in the firststage, followed by a homometathesis, finished off by the hydrogenation.Ricinoleic (12-hydroxy-cis-9-octadecenoic) acid is, for its part,subjected to a pyrolysis which makes possible the synthesis ofω-undecenoic acid, which is subjected to a cross-metathesis with acrylicacid giving 11-dodecenedioic acid, converted by hydrogenation tododecanedioic acid.

The reaction mechanism for this reaction with petroselinic acid (scheme2) is as follows.

CH₃—(CH₂)₁₀—CH═CH—(CH₂)₄—COOH+CH₂═CH₂

CH₂═CH—(CH₂)₄—COOH+CH₂═CH—(CH₂)₁₀—CH₃  1)

2)2CH₂═CH—(CH₂)₄—COOH

HOOC—(CH₂)₄—CH═CH—(CH₂)₄—COOH+CH₂═CH₂  2)

HOOC—(CH₂)₄—CH═CH—(CH₂)₄—COOH+H₂→HOOC—(CH₂)₁₀—COOH  3)

The reaction process with ricinoleic acid is as follows:

CH₃—(CH₂)₅—CHOH—CH₂—CH═CH—(CH₂)₇—COOH(Δ)→CH₃—(CH₂)₅—CHO+CH₂═CH—(CH₂)₈—COOH  1)

CH₂═CH—(CH₂)₈COOH+HOOC—CH═CH₂

HOOC—CH═CH—(CH₂)₈—COOH+CH₂═CH₂  2)

HOOC—CH═CH—(CH₂)₈COOH+H₂→HOOC—(CH₂)₁₀—COOH.  3

The C₁₂ diacid can also be obtained by ethenolysis of oleic acid, togive the unsaturated acid CH₂═CH—(CH₂)₇—COOH, followed by across-metathesis with the acid CH₃—CH═CH—CH₂—COOH and, finally, by ahydrogenation.

The C₁₃ diacid can be obtained from vaccenic (cis-11-octadecenoic) acid,gondoic (cis-11-eicosenoic) acid and cetoleic (cis-11-docosenoic) acidwith an ethenolysis in the first stage, followed by a cross-metathesiswith acrylic acid, in each case brought to completion by ahydrogenation.

The C₁₄ diacid can be obtained from lesquerolic acid with a pyrolysis ofthe hydroxylated fatty acid to form the acid of formulaCH₂═CH—(CH₂)₁₀—COOCH₃, followed by a cross-metathesis with acrylic acidand, finally, by a hydrogenation. It can also be obtained by ethenolysisof vaccenic acid, to give the unsaturated acid CH₂═CH—(CH₂)_(g)—COOH,followed by a cross-metathesis with the acid CH₃—CH═CH—CH₂—COOH and,finally, by a hydrogenation.

The C₁₅ diacid can be obtained from erucic acid with an ethenolysis inthe first stage, followed by a cross-metathesis with acrylic acid,brought to completion by a hydrogenation.

The C₁₆ diacid can be obtained from nervonic acid with an ethenolysis inthe first stage, followed by a cross-metathesis with acrylic acid,brought to completion by a hydrogenation.

It is entirely possible, if need be, to manufacture higher diacids byemploying the process of the invention, for example C₁₈, C₂₀, C₂₂ or C₂₆diacids.

The invention also relates to a process for the synthesis of the diacidor the diester of formula ROOC—(CH₂)₈—COOR from 5-lauroleic or5-physeteric acid or ester with, in the first stage, an ethenolysis ofsaid acid or said ester, to produce the acid or the ester of formulaCH₂═CH—(CH₂)₃—COOR, followed by a homometathesis, finished off byhydrogenation.

Metathesis reactions have been known for a long time, even if theirindustrial applications are relatively limited. Reference may be made,with regard to their use in the conversion of fatty acids (esters), tothe paper by J. C. Mol, “Catalytic metathesis of unsaturated fatty acidesters and oil”, which appeared in Topics in Catalysis, Vol. 27, Nos.1-4, February 2004 (Plenum Publishing Corporation).

The catalysis of the metathesis reaction has formed the subject of agreat many studies and the development of sophisticated catalyticsystems. Mention may be made, for example, of the tungsten complexesdeveloped by Schrock et al., J. Am. Chem. Soc., 108 (1986), 2771, orBasset et al., Angew. Chem., Ed. Engl., 31 (1992), 628. More recently,“Grubbs” catalysts, which are ruthenium-benzylidene complexes, haveappeared (Grubbs et al., Angew. Chem., Ed. Engl. 34 (1995), 2039, andOrganic Lett., 1 (1999), 953). These relate to homogeneous catalysis.Heterogeneous catalysts have also been developed which are based onmetals, such as rhenium, molybdenum and tungsten, deposited on aluminaor silica. Finally, studies have been carried out on the preparation ofimmobilized catalysts, that is to say of catalysts whose activeprinciple is that of the homogeneous catalyst, in particularruthenium-carbene complexes, but which is immobilized on an inactivesupport. The object of these studies is to increase the selectivity ofthe reaction with regard to the side reactions, such as“homometatheses”, between the reactants brought together. They relatenot only to the structure of the catalysts but also to the effect of thereaction medium and the additives which may be introduced.

Any active and selective metathesis catalyst can be used in the processof the invention. However, use will preferably be made of catalystsbased on ruthenium and on rhenium.

The ethenolysis (metathesis) reaction of the first stage is carried outat a temperature of between 20 and 100° C. at a pressure of 1 to 30 barin the presence of a conventional metathesis catalyst. The reaction timeis chosen according to the reactants employed and in order to reach, tothe nearest point, the equilibrium of the reaction. The reaction iscarried out under an ethylene pressure.

The pyrolysis reaction of the first stage is carried out at atemperature generally of between 400 and 600° C.

The homometathesis reaction of the second stage is carried out at atemperature generally of between 20 and 200° C. in the presence of aconventional metathesis catalyst.

The cross-metathesis reaction of the second stage is carried out at atemperature generally of between 20 and 200° C. in the presence of aruthenium-based catalyst.

The hydrogenation reaction of the third stage is carried out at atemperature generally of between 20 and 300° C. under hydrogen pressurein the presence of a catalyst comprising, for example, nickel, cobalt,platinum or palladium, and the like. The process of the invention isillustrated by the following examples.

EXAMPLE 1

This example illustrates the synthesis of the C₁₁ diacid starting fromoleic acid. In a first stage, the ethenolysis of oleic acid is carriedout at 30° C. in the presence of a tungsten-based catalyst in order toobtain 9-decenoic acid CH₂═CH—(CH₂)₇—COOH. For the second stage, use ismade of the bispyridine ruthenium complex (8) catalyst described in thepublication by Chen-Xi Bei et al., Tetrahedron Letters, 46 (2005),7225-7228, in carrying out the cross-metathesis of 9-decenoic acid withmethyl acrylate. The reaction is carried out in CH₂Cl₂, at a 0.1M9-decenoic acid concentration and a 0.2M methyl acrylate concentration,at a temperature of 50° C. and for 12 hours. The yields are determinedby chromatographic analysis. In the present case, use is made of 2equivalents of methyl acrylate with respect to the acid and with acatalyst concentration of 0.5 mol %. The yield of productCH₃—OOC—CH═CH—(CH₂)₇—COOH is 50 mol %. This product can be hydrogenatedaccording to a conventional process with a yield of 100%.

EXAMPLE 2

This example illustrates the synthesis of the C₂₀ diacid starting fromricinoleic acid. During the first stage, methyl ricinoleate is subjectedto a pyrolysis at a temperature of 550° C. to form methyl10-undecenoate, which is converted to the acid form by hydrolysis. Inthe second homometathesis stage, use is made of the ruthenium complex(3) catalyst described in the publication by Stefan Randl et al.,Synleft (2001), 10, 430, which is very stable and does not decomposewhen it is exposed to air or to water. The homometathesis reaction iscarried out in CH₂Cl₂, at a 0.15M 10-undecenoic acid concentration, at atemperature of 30° C. and for 2 hours with a catalyst concentration of0.5 mol %. The yields are determined by chromatographic analysis. Theyield of diacid HOOC—(CH₂)₈—CH═CH—(CH₂)₈—COOH is 67 mol %. This productcan be hydrogenated according to a conventional process with a yield of100%.

EXAMPLE 3

This example illustrates the synthesis of the C₁₂ diacid starting fromricinoleic acid. The first stage is identical to that of example 2,apart from the condition that it is the methyl ester of 10-undecenoicacid CH₂═CH—(CH₂)₈—COOCH₃ which is addressed in the second stage. Thissecond stage is a cross-metathesis with methyl acrylate. Use is made,for this reaction, of the bispyridine ruthenium complex (8) catalystdescribed in the publication by Chen-Xi Bai et al., Org. Biomol. Chem.(2005), 3, 4139-4142. The reaction is carried out in CH₂Cl₂, at a 0.05Mmethyl ester of 10-undecenoic acid concentration and a 0.1M methylacrylate concentration, at a temperature of 30° C. and for 12 hours inthe presence of the catalyst at a concentration of 1 mol %, with respectto the methyl ester of 10-undecenoic acid. The yields are determined bychromatographic analysis. The yield of diesterCH₃—OOC—CH═CH—(CH₂)₈—COOCH₃ is 70 mol %. This product, in its ester oracid form, can be hydrogenated according to a conventional process witha yield of 100%.

This example thus illustrates a process for the synthesis of the diesterof formula CH₃OOC—(CH₂)₈—COOCH₃ starting from the methyl ester ofricinoleic acid subjected, in the first stage, to a pyrolysis, in orderto form the ester of formula CH₂═CH—(CH₂)₈—COOCH₃, which is subsequentlysubjected to a cross-metathesis with methyl acrylate forming the diesterof formula CH₃OOC—CH═CH—(CH₂)₈—COOCH₃, which is subsequentlyhydrogenated.

EXAMPLE 4

The metathesis catalysts A and B were obtained from Sigma Aldrich,catalogue references 569747 and 569755 respectively. These catalysts arealso known as Grubbs catalyst, 2nd generation, and Hoveyda-Grubbscatalyst, 2nd generation.

Catalyst A: benzylidene[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene]dichloro(tri-cyclohexyphosphine)ruthenium.Catalyst B:(3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(o-isopropoxy-phenylmethylene)ruthenium.

Undecylenic acid is produced by Arkema by hydrolysis of the methyl esterof undecylenic acid, itself obtained by cracking the methyl ester ofricinoleic acid. The latter is obtained by transesterification of castoroil by methanol in basic catalysis. These products are produced in theArkema factory at Marseille Saint-Menet.

In the experiments, 2.5 g of ester of fatty acid (undecylenic acid)and/or an excess of methyl acrylate are used. Tetradecane is used asinternal standard. The reaction mixture is stirred at 50° C. anddegassed with argon. The catalyst is added to the solution, withoutaddition of solvent. The samples of reaction products are analyzed bychromatography.

Examples N and M below illustrate the case of the homometathesis ofmethyl undecylenate and example O illustrates the case of thecross-metathesis of methyl undecylenate and methyl acrylate.

Cross- Methyl acrylate/methyl Homometathesis metathesis ReactionCatalyst undecylenate molar Conversion yield yield time Example (mol %)ratio mol % mol % mol % min N A (1) 0 98 100 0 30 M B (1) 0 95 100 0 30O B (0.1) 10 99 0 99 30

1) A process for the synthesis of diacids or diesters of the generalformula ROOC—(CH₂)_(x)—COOR, in which x represents an integer between 5and 24 and R is either H or an alkyl radical of 1 to 4 carbon atoms,starting from long-chain natural monounsaturated fatty acids or esterscomprising at least 10 adjacent carbon atoms per molecule, of theformula CH₃—(CH₂)_(n)—CHR₁—CH₂—CH═CH—(CH₂)_(p)—COOR, in which Rrepresents H or an alkyl radical comprising from 1 to 4 carbon atoms, R₁is either H or OH, and n and p, which are identical or different, areindices between 3 and 11, which comprises: converting said naturalmonounsaturated fatty acid or ester, into an ω-monounsaturated fattyacid or ester of the general formula CH₂═CH—(CH₂)_(m) COOR, in which mis equal to p or p+1, then, subjecting the product thus obtained to ametathesis reaction, selected from homometathesis, in order to obtain acompound of the formula ROOC—(CH₂)_(m)—CH═CH—(CH₂)_(m)—COOR, orcross-metathesis with a compound of the formulaR₂OOC—(CH₂)_(r)—CH═CH—R₃, in which R₂ is either H or an alkyl radicalcomprising from 1 to 4 carbon atoms, r is either 0 or 1 or 2 and R₃ isH, CH₃ or COOR₂, in the last case forming a cyclic or noncyclicmolecule, to obtain an unsaturated compound of the formulaROOC—(CH₂)_(m)—CH═CH—(CH₂)_(r)—COOR₂, and then, converting, byhydrogenation, the unsaturated compound to give a saturated compound. 2)The process as claimed in claim 1, characterized in that converting saidnatural monounsaturated fatty acid or ester of general formulaCH₃—(CH₂)_(n)—CHOH—CH₂—CH═CH—(CH₂)_(p)—COOR to via a pyrolysis reaction.3) The process as claimed in claim 2, characterized in that theco-monounsaturated acid or the ester of formula CH₂═CH—(CH₂)_(p+1)—COORis subjected to a homometathesis, the product of which,ROOC—(CH₂)_(p+1)—CH═CH—(CH₂)_(p+1)—COOR is hydrogenated. 4) The processas claimed in claim 2, characterized in that the ω-monounsaturated acidor the ester of formula CH₂═CH—(CH₂)_(p+1)—COOR resulting from the firststage is subjected to a cross-metathesis, the product of which ishydrogenated. 5) The process as claimed in claim 1, characterized inthat converting said natural monounsaturated fatty acid or ester ofgeneral formula CH₃—(CH₂)_(n)—CHOH—CH₂—CH═CH—(CH₂)_(p)—COOR to via anethenolysis reaction. 6) The process as claimed in claim 5,characterized in that the ω-monounsaturated acid or the ester of formulaC₂═CH—(CH₂)_(p)—COOR is subjected to a homometathesis, the product ofwhich, ROOC—(CH₂)_(p)—CH═CH—(CH₂)_(p)—COOR, is hydrogenated. 7) Theprocess as claimed in claim 5, characterized in that theω-monounsaturated acid or the ester of formula CH₂═CH—(CH₂), —COOR issubjected to a cross-metathesis, the product of which is hydrogenated.8) A process for the synthesis of a diester of the formulaC₁₃OOC—(C₂)₈—COOCH₃ starting from the methyl ester of ricinoleic acidcomprising pyrolysis, to form an ester of the formulaCH₂═CH—(CH₂)₈—COOCH₃, and subsequently cross-metathesis with methylacrylate to form a diester of the formula C₃OOC—CH═CH—(CH₂)₈—COOCH₃,which is subsequently hydrogenated. 9) A process for the synthesis ofthe diester of the formula CH₃OOC—(CH₂)₁₂—COOCH₃ starting from themethyl ester of lesquerolic acid comprising pyrolysis of the methylester of lesquerolic acid to form an ester of the formulaCH₂═CH—(CH₂)₁₀—COOCH₃, followed, by cross-metathesis with methylacrylate and, thereafter hydrogenation. 10) A process for the synthesisof a diacid or diester of formula ROOC—(CH₂)₁₂—COOR starting fromvaccenic acid or ester comprising ethenolysis of thin the acid or esterto give an unsaturated acid or ester of the formula CH₂═CH—(CH₂)₉—COOR,followed by cross-metathesis with an acid or ester of the formulaCH₃—CH═CH—CH₂—COOR and, thereafter hydrogenation. 11) A process for thesynthesis of a diacid or diester of formula ROOC—(CH₂)₈—COOR startingfrom 5-lauroleic or 5-physeteric acid or ester comprising ethenolysis ofsaid acid or said ester to produce an acid or ester of the formulaCH₂═CH—(CH₂)₃—COOR, followed by homometathesis followed byhydrogenation.